99431 ÷ 8 = 12428 R7
We're going to perform division on 99431 with 8 as the divisor.

Step 1:
8 goes into 9 1 times with a remainder of 1.
Write down 1 as next digit of of the result. 
Result so far: 1
Subtract 8 from 9 to get 1.
Bring next digit (9) of the dividend behind the 1 and repeat the process: 19 / 8

Step 2:
8 goes into 19 2 times with a remainder of 3.
Write down 2 as next digit of of the result. 
Result so far: 12
Subtract 16 from 19 to get 3.
Bring next digit (4) of the dividend behind the 3 and repeat the process: 34 / 8

Step 3:
8 goes into 34 4 times with a remainder of 2.
Write down 4 as next digit of of the result. 
Result so far: 124
Subtract 32 from 34 to get 2.
Bring next digit (3) of the dividend behind the 2 and repeat the process: 23 / 8

Step 4:
8 goes into 23 2 times with a remainder of 7.
Write down 2 as next digit of of the result. 
Result so far: 1242
Subtract 16 from 23 to get 7.
Bring next digit (1) of the dividend behind the 7 and repeat the process: 71 / 8

Step 5:
8 goes into 71 8 times with a remainder of 7.
Write down 8 as next digit of of the result. 
Result so far: 12428
Subtract 64 from 71 to get 7.

The final result is 12428 with a remainder of 7.